a. This is a great technique to keep in mind when arguing with narcissistic people.

Is that sentence slightly ambiguous?

Is it a great technique per se which is to be used when you are arguing with narcissistic people? ( [a great technique] which is to be used...) Maybe it is also a great technique for arguing with other types of people.

Or is it a great technique only when arguing with narcissistic people?

Would a comma after 'a great technique' change anything?

b. This is a great technique**,** to use when arguing with narcissistic people.

Many thanks.

a. This is a great technique to keep in mind when arguing with narcissistic people.

Is that sentence slightly ambiguous?

Is it a great technique per se which is to be used when you are arguing with narcissistic people? ( [a great technique] which is to be used...) Maybe it is also a great technique for arguing with other types of people.

Or is it a great technique only when arguing with narcissistic people?

Would a comma after 'a great technique' change anything?

b. This is a great technique , to use when arguing with narcissistic people.

Many thanks.